Not my finest moment. But funny as hell.

Back when I was in my mid 20's I bought my first place to live. Nothing great, it was just a trailer house, but it was mine. My neighbors were ok for the first few months. Then one day I was hearing banging on my walls. The kids on one side were using my outside wall to constantly bounce tennis balls off. It drove me nuts. Talked to the neighbor. They said "kids will be kids" and didn't put a stop to it. I decided it's time to do something after a few days and got a set of extremely loud air horns like they use on trains and semi trucks. Put them under the skirting. The next time the kids started I hooked up the air hose from my air compressor and opened the valve. The kids screamed and ran crying. I was crying from laughing so hard. The parents were pissed and came over making threats and yelling at me. The second petty revenge I got was one night I hid a wireless battery powered doorbell under their stairs and id randomly push button to ring it. Their dogs would go crazy barking and running around. I changed the batteries that thing about a dozen times I used so much.